Printed circuit board for optical waveguide and method of manufacturing the same

ABSTRACT

Disclosed herein is a printed circuit board for an optical waveguide, including a base board, and an optical waveguide formed on the base board. The optical waveguide includes a lower clad layer formed on the base board, an insulation layer formed on the lower clad layer and having a core-forming through-hole, a core part formed on a region of the lower clad layer, which is exposed through the through-hole, and an upper clad layer formed in the through-hole and on the insulation layer.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of Korean Patent Application No.10-2008-0022923, filed Mar. 12, 2008, entitled “PRINTED CIRCUIT BOARDFOR OPTICAL WAVEGUIDES AND METHOD OF MANUFACTURING THE SAME”, which ishereby incorporated by reference in its entirety into this application.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a printed circuit board for an opticalwaveguide and a method of manufacturing the same, and more particularlyto a printed circuit board for an optical waveguide and a method ofmanufacturing the same, which is capable of being used to efficientlymanufacture an optical waveguide using a relatively small amount of corematerial, compared to a conventional process, by locally applying corematerial only on the area of a lower clad layer, which is exposedthrough a through-hole of an insulation layer, and forming a core partthrough patterning.

2. Description of the Prior Art

These days, the demand for optical substrates, including variouswirings, which enable electrical signals or optical signals to betransmitted to mobile devices or network devices requiring high-speeddata transmission, is rapidly increasing.

Optical transmission wires, which are typically produced using polymermaterial having low light transmission, are each comprised of a corepart, through which signals are transmitted and which has a squaresection having a thickness of 50 μm, and a clad part, enveloping thecore part. The square sectional core part is typically manufacturedusing a photo-etching technique.

Referring to FIGS. 4A to 4C, a conventional method of manufacturing aprinted circuit board for an optical waveguide will be described.

First, a flexible substrate is comprised of a copper layer 11 and apolyimide layer 12, and a lower clad layer 13 and a core layer 14 aresequentially formed on the polyimide layer 12 of the flexible substrate(see FIG. 4A).

Then, the core layer 14 is patterned through a typical photo-etchingprocess, to thus form a core part 14 a (see FIG. 4B).

Finally, an upper clad layer 15 is formed on the lower clad layer 13, onwhich the core part 14 a is formed, thus providing a printed circuitboard for an optical waveguide (see FIG. 4C).

According to the above-described conventional method, a core material isapplied to the entire work surface of the substrate, to thus form thecore layer 14, and the core material is patterned through light exposureand development, to thus form the core part 14 a. Accordingly, theconventional method has a disadvantage in that a relatively large amountof core material is removed, compared to the amount required forformation of the core part 14 a, thus increasing material costs. Inparticular, taking into consideration the high cost of optical wiringmaterial, an economic and efficient method that is capable of being usedto manufacture an optical substrate is desperately required.

SUMMARY OF THE INVENTION

Accordingly, the present inventor has made extensive studies to solvethe above-described problems occurring in the prior art, and, as aresult, has found a method of efficiently manufacturing an opticalwaveguide using a relatively small amount of core material, compared toa conventional process, by locally applying core material only on thearea of a lower clad layer, which is exposed through a through-hole ofan insulation layer, and forming a core part through patterning. Basedon the finding, the present invention is accomplished.

Accordingly, in an aspect, the present invention provides a printedcircuit board for an optical waveguide and a method of manufacturing theprinted circuit board, which is capable of minimizing the amount of corematerial that is removed by the patterning in the formation of the corepart.

In another aspect, the present invention provides a method ofefficiently manufacturing a printed circuit board for an opticalwaveguide with a high degree of freedom in the selection of materials.

In a further aspect, the present invention provides a method ofefficiently manufacturing a printed circuit board for an opticalwaveguide, which has high reliability.

According to an aspect, the present invention provides a printed circuitboard for an optical waveguide, including: a base board; and an opticalwaveguide formed on the base board, wherein the optical waveguideincludes: a lower clad layer formed on the base board; an insulationlayer formed on the lower clad layer and having a core-formingthrough-hole; a core part formed on a region of the lower clad layer,which is exposed through the through-hole; and an upper clad layerformed in the through-hole and on the insulation layer.

The base board may include any one of a metal layer for forming acircuit, a rigid printed circuit board, a flexible printed circuit boardand a rigid-flexible printed circuit board.

The insulation layer may be selected from a group consisting of athermosetting resin, a thermoplastic resin, a reinforcingmaterial-impregnated thermosetting resin, a reinforcingmaterial-impregnated thermoplastic resin, and a combination thereof.

The core part may include a plurality of core patterns, and the corepart may have a height equal to or higher than a height of theinsulation layer.

According to another aspect, the present invention provides a method ofmanufacturing a printed circuit board for an optical waveguide,including: forming a lower clad layer on a base board; forming aninsulation layer, having a core-forming through-hole therein, on thelower clad layer; filling the through-hole in the insulation layer witha core material; forming a core part by patterning the core materialreceived in the through-hole; and forming an upper clad layer in thethrough-hole and on the insulation layer.

The forming the core part may include: layering a transparent releasablefilm on the insulation layer having the through-hole filled with thecore material, to thus flatten the core material; selectively exposingthe core material through a pattern mask; and removing the transparentreleasable film and developing the exposed core material, thus forming aplurality of core patterns.

The transparent releasable film may include polyethylene terephthalate.

According to an embodiment, the forming an insulation layer may include:layering the insulation layer on the lower clad layer; and removing aportion of the insulation layer to form the core-forming through-hole.

According to another embodiment, the forming an insulation layer mayinclude: preparing the insulation layer; removing a portion of theinsulation layer to form the core-forming through-hole; and layering theinsulation layer having the core-forming through-hole on the lower cladlayer.

According to a further aspect, the present invention provides a methodof manufacturing a printed circuit board for an optical waveguide,including: forming a lower clad layer on a base board; forming a moldingfilm, having a core-forming through-hole therein, on the lower cladlayer; filling the through-hole in the molding film with a corematerial; forming a core part by patterning the core material receivedin the through-hole; removing the molding film; and forming an upperclad layer on the lower clad layer such that the upper clad layersurrounds the core part.

The forming a core part may include: layering a transparent releasablefilm on the molding film having the through-hole filled with the corematerial, to thus flatten the core material; selectively exposing thecore material through a pattern mask; and removing the transparentreleasable film and developing the exposed core material, thus forming aplurality of core patterns.

The forming a molding film may include: layering the molding film on thelower clad layer; and removing a portion of the molding film to form thecore-forming through-hole.

The molding film may include a photo-sensitive resist film or areleasable film.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the presentinvention will be more clearly understood from the following detaileddescription taken in conjunction with the accompanying drawings, inwhich:

FIGS. 1A to 1J are process views illustrating a method of manufacturinga printed circuit board for an optical waveguide, according to a firstpreferred embodiment of the present invention;

FIGS. 2A to 2I are process views illustrating a method of manufacturinga printed circuit board for an optical waveguide, according to a secondpreferred embodiment of the present invention;

FIGS. 3A to 3K are process views illustrating a method of manufacturinga printed circuit board for an optical waveguide, according to a thirdpreferred embodiment of the present invention; and

FIGS. 4A to 4C are process views illustrating a conventional method ofmanufacturing a printed circuit board for an optical waveguide.

DETAILED DESCRIPTION OF THE INVENTION

This invention will be described in further detail with reference toexamples and to the accompanying drawings, but the present invention isnot limited to this description.

FIGS. 1A to 1J are process views illustrating a method of manufacturinga printed circuit board for an optical waveguide, according to a firstpreferred embodiment of the present invention, FIGS. 2A to 2I areprocess views illustrating a method of manufacturing a printed circuitboard for an optical waveguide, according to a second preferredembodiment of the present invention, and FIGS. 3A to 3K are processviews illustrating a method of manufacturing a printed circuit board foran optical waveguide, according to a third preferred embodiment of thepresent invention.

Referring to FIGS. 1A to 1J, a method of manufacturing a printed circuitboard for an optical waveguide, according to a first preferredembodiment of the present invention, is described.

First, a flexible copper clad laminate functioning as a base board iscomprised of a copper layer 101 and a polyimide layer 102, and a lowerclad layer 103 is formed on the polyimide layer 102 of the flexiblecopper clad laminate (see FIG. 1A).

Although the flexible copper clad laminate is illustrated as a baseboard in these drawings, which incorporated the polyimide layer thereinas an insulation layer, the material of the base board is notparticularly limited to the flexible copper clad laminate. In this case,a circuit-forming metal layer, such as a copper thin film, may bedirectly applied, or other flexible copper clad laminate, rigid copperclad laminate or rigid-flexible copper clad laminate, which isdominantly used in the field of the printed circuit board, may beapplied if necessary. Further, as the base board, a flexible printedcircuit board, a rigid printed circuit board or a rigid-flexible printedcircuit board, in which one or more circuit layers are previouslyformed, may be used.

Although the lower clad layer 103 is typically prepared by layering ausual clad film on the base board, the lower clad layer is notparticularly limited thereto, and may be prepared using any of thecommonly-known processes such as a coating.

Then, an insulation layer 104 is formed on the lower clad layer 103 (seeFIG. 1B), and a portion of the insulation layer 104 is removed, to thusform a through-hole 105, in which a core is to be formed (see FIG. 1C).

The insulation layer 104 may be made of one of thermosetting resin,thermoplastic resin, reinforcing material-impregnated thermosettingresin and reinforcing material-impregnated thermoplastic resin, or acombination of two or more thereof. Concrete examples of the insulationlayer 104 may include a prepreg, a polyimide film and a photo-sensitiveinsulation material, but the invention is not particularly limited tothe above-listed materials.

The process of forming the through-hole 105 in the insulation layer 104is not particularly limited, but may be suitably selected depending onthe material of the insulation layer that is actually used. For example,the through-hole 105 may be formed through a photo-etching process usinglight exposure/development, a laser machining process or the like.

Subsequently, the through-hole 105 of the insulation layer 104 is filledwith a core material 106 (see FIG. 1D).

The filling operation of the through-hole 105 with the core material 106may be conducted using any of processes known in the art, such asdispensing, ink jetting and printing, and the core material 106 chargedin the through-hole 105 may be cured using a pre-baking process.However, the process of preparing the core material 106 is notparticularly limited to these. The core material 106, which is chargedin the through-hole through the above-described process, may bulgeupwards to be convex, depending on the kind and the charging amount ofthe core material.

Then, the core material 106 charged in the through-hole 105 is subjectedto a patterning process, thus forming a core part 106 a (see FIG. 1H).

In the preferred embodiment, the formation of the core part 106 a may beconducted in the manner described below.

First, a transparent releasable film 107 is layered on the insulationlayer 104, having the through-hole 105 filled with the core material106, in the vacuum atmosphere, so that the core material 106 charged inthe through-hole 105 is flattened (see FIG. 1E). As the transparentreleasable film 107 used in this process, any material that functions toprevent contamination caused by extraneous substances and to flatten thecore material, and that further functions to allow the transmission oflight in the subsequent light exposure process and to allow easyelimination thereof after the light exposure, may be used withoutlimitation. For example, polyethylene terephthalate (PET) may bepreferably used.

Then, a pattern mask 108 having a predetermined patterning shape isplaced on the transparent releasable film 107, so as to selectivelyexpose the core material 106 to light (see FIG. 1F). At this point, postexposure baking (PEB) may be optionally conducted before or after thelight exposure, if necessary.

Subsequently, the transparent releasable film 107 is removed (see FIG.1G), and the core material 106, which is exposed to light, is developed,to thus form a plurality of core parts 106 a (see FIG. 1H). The coreparts 106 a, which are obtained using the above processes, may have aheight which is equal to or higher than the height of the insulationlayer 104, depending on the results of the charging of the core materialand the flattening process.

Finally, an upper clad layer 109 is applied in the rest through-hole 105except for the core part 106 a and on the insulation layer 104 (see FIG.11). Thereafter, the copper layer 101 of the flexible copper cladlaminate, which is used as the base board, is patterned to thus have adesired circuit pattern 101 a, as necessary (see FIG. 1J).

Although the upper clad layer 109 is typically formed by layering a cladfilm in the vacuum atmosphere, it may be formed through any other knownprocess, such as coating process, without limitation to the abovespecified process.

Referring to FIGS. 2A to 2I, a method of manufacturing a printed circuitboard for an optical waveguide, according to a second preferredembodiment of the present invention, is described.

This second embodiment is substantially identical to the firstembodiment, with the exception that the through-hole is formed inadvance before the layering of a lower clad layer in a formation of aninsulation layer having a through-hole. Therefore, a description thereofwill be briefly provided below, obviating detail therefrom.

First, a flexible copper clad laminate functioning as a base board iscomprised of a copper layer 201 and a polyimide layer 202, and a lowerclad layer 203 is formed on the polyimide layer 202 of the flexiblecopper clad laminate (see FIG. 2A).

An insulation layer 204, having a plurality of through-holes 205 adaptedto form cores, is prepared, and is then layered on the lower clad layer203 (see FIG. 2B).

The process of forming the through-holes 205 in the insulation layer 204is not particularly limited, but may be properly selected depending onthe material of the insulation layer 204 which is actually used. Forexample, the through-holes 205 may be formed through a punching or arouting process.

Subsequently, the through-hole 205 of the insulation layer 204 is filledwith a core material 206 (see FIG. 2C).

Then, the core material 206 charged in the through-hole 205 is subjectedto a patterning process, thus forming a core part 206 a (see FIG. 2G).

In the preferred embodiment, the formation of the core part 206 a may beconducted in the manner described below.

First, a transparent releasable film 207 is layered on the insulationlayer 204, having the through-hole 205 filled with the core material206, in the vacuum atmosphere, so that the core material 206 charged inthe through-hole 205 is flattened (see FIG. 2D).

Then, a pattern mask 208 having a predetermined patterning shape isplaced on the transparent releasable film 207, so as to selectivelyexpose the core material 206 to light (see FIG. 2E). At this point, postexposure baking (PEB) may be optionally conducted before or after thelight exposure, if necessary.

Subsequently, the transparent releasable film 207 is removed (see FIG.2F), and the core material 206, which is exposed to light, is developed,to thus form a plurality of core parts 206 a (see FIG. 2G). The coreparts 206 a, which are obtained using the above processes, may have aheight which is equal to or higher than the height of the insulationlayer 204, depending on the results of the charging of the core materialand the flattening process.

Finally, an upper clad layer 209 is applied in the rest through-hole 205except for the core part 206 a and on the insulation layer 204 (see FIG.2H). Thereafter, the copper layer 201 of the flexible copper cladlaminate, which is used as the base board, is patterned to thus have adesired circuit pattern 201 a, as necessary (see FIG. 2I).

Referring to FIGS. 3A to 3K, a method of manufacturing a printed circuitboard for an optical waveguide, according to a third preferredembodiment of the present invention, is described.

This third embodiment is conducted in the same process as those of theabove first and second embodiments, with the exception that a moldingfilm having a through-hole is used to form a core, and is then removedafter the formation of the core, by which no molding film remains on thefinal product, unlike the first and second embodiments, in which theinsulation layer having the through-hole adapted to form the core isused and remains on the final product. Therefore, a description thereofwill be briefly provided hereinafter, without a detailed descriptionthereof.

First, a flexible copper clad laminate functioning as a base board iscomprised of a copper layer 301 and a polyimide layer 302, and a lowerclad layer 303 is formed on the polyimide layer 302 of the flexiblecopper clad laminate (see FIG. 3A).

An molding film 304, having a through-hole 305 adapted to form a core,is prepared, and is then layered on the lower clad layer 303 (see FIG.3C).

Preferably, a molding film 304, which is easy to remove, is layered onthe lower clad layer 303 (see FIG. 3B), and then a predetermined portionadapted to form a core is removed from the molding film 304, thusproviding a through-hole 305 (see FIG. 3C).

The molding film 304 may include, but is not limited to, a typicalphoto-sensitive film such as a dry film, and a releasable film, so thatit is easily removed in the subsequent process.

The process of forming the through-hole 305 in the molding film 304 isnot particularly limited, but may be properly selected depending on thematerial of the molding film that is actually used. For example, in caseof using a dry film, the through-hole of the molding film may be formedby locally removing the molding film through a usual photo-etchingprocess using light exposure/development.

Subsequently, the through-hole 305 of the molding film 304 is filledwith a core material 306 (see FIG. 3D).

Then, the core material 306 charged in the through-hole 305 is subjectedto a patterning process, thus forming a core part 306 a (see FIG. 3H).

In the preferred embodiment, the formation of the core part 306 a may beconducted in the manner described below.

First, a transparent releasable film 307 is layered on the molding film304, having the through-hole 305 filled with the core material 306, inthe vacuum atmosphere, so that the core material 306 charged in thethrough-hole 305 is flattened (see FIG. 3E). As the transparentreleasable film 307 used in this process, any material that functions toprevent contamination caused by extraneous substances and to flatten thecore material, and that further functions to allow transmission of lightin the subsequent light exposure process and to allow easy eliminationthereof after the light exposure, may be used without limitation. Forexample, polyethylene terephthalate (PET) may be preferably used.

Then, a pattern mask 308 having a predetermined patterning shape isplaced on the transparent releasable film 307, so as to selectivelyexpose the core material 306 to light (see FIG. 3F). At this point, postexposure baking (PEB) may optionally be conducted before or after thelight exposure, if necessary.

Subsequently, the transparent releasable film 307 is removed (see FIG.3G), and the core material 306, which is exposed to light, is developed,to thus form a plurality of core parts 306 a (see FIG. 3H).

After the formation of the core part 306 a through the patterning of thecore material 306, the molding film 304 is removed (see FIG. 3I). Theprocess of removing the molding film 304 may be properly selecteddepending on the material of the molding film 304 that is actually used.For example, in the case of using a dry film, the dry film may beremoved using a stripping technique known in the art.

Finally, an upper clad layer 309 is applied on the lower clad layer 303such that the upper clad layer 309 surrounds the core part 306 a (seeFIG. 3J). Thereafter, the copper layer 301 of the flexible copper cladlaminate, which is used as the base board, is patterned to thus have adesired circuit pattern 301 a, if necessary (see FIG. 3K).

Although the upper clad layer 309 is typically formed through layeringof a clad film in the vacuum atmosphere, the process of forming theupper clad layer is not limited thereto, but may be formed using anyknown process, such as coating.

As described above, according to the present invention, a core materialis applied on only a restricted region, i.e., in only a through-hole ofa core-forming member, without the application of core material to theentire work size of a printed circuit board, and is patterned to thusform a core part. As a result, the amount of core material can bereduced to about 1/10 to 1/50 of the amount of core material used in aconventional method, thus improving economic efficiency.

Further, the invention is advantageous in that the member having thethrough-hole is constructed using a material that is typically used inthe manufacture of printed circuit boards, and is then removed duringthe manufacturing process or remains on the final product, thus enablingsomewhat free selection of materials for products and the free design ofproducts.

In addition, thanks to the use of the insulation member having thethrough-hole and the use of the optional transparent releasable film,the present invention enables the formation of more precise and finecore parts and can avoid the deteriorations of optical properties due topoor flatness of the core part and the infiltration of extraneoussubstances, thus enabling the efficient production of a highly reliableprinted circuit board for an optical waveguide.

Although the preferred embodiments of the present invention have beendisclosed for illustrative purposes, a printed circuit board for anoptical waveguide and a method of manufacturing the same, according tothe present invention, is not limited to these embodiments, and thoseskilled in the art will appreciate that various modifications, additionsand substitutions are possible, without departing from the scope andspirit of the invention as disclosed in the accompanying claims.

Simple changes and modifications of the present invention also fallwithin the scope of the present invention, and the true scope ofprotection of the present invention will be defined by the accompanyingclaims.

1. A printed circuit board for an optical waveguide, comprising: a baseboard; and an optical waveguide formed on the base board, wherein theoptical waveguide comprises: a lower clad layer formed on the baseboard; an insulation layer formed on the lower clad layer and having acore-forming through-hole; a core part formed on a region of the lowerclad layer, which is exposed through the through-hole; and an upper cladlayer formed on side portions of the core part and on the insulationlayer.
 2. The printed circuit board for an optical waveguide, accordingto claim 1, wherein the base board includes any one of a metal layer forforming a circuit, a rigid printed circuit board, a flexible printedcircuit board and a rigid-flexible printed circuit board.
 3. The printedcircuit board for an optical waveguide, according to claim 1, whereinthe insulation layer is selected from a group consisting of athermosetting resin, a thermoplastic resin, a reinforcingmaterial-impregnated thermosetting resin, a reinforcingmaterial-impregnated thermoplastic resin, and a combination thereof. 4.The printed circuit board for an optical waveguide, according to claim1, wherein the core part comprises a plurality of core patterns.
 5. Theprinted circuit board for an optical waveguide, according to claim 1,wherein the core part has a height equal to or higher than a height ofthe insulation layer.
 6. A method of manufacturing a printed circuitboard for an optical waveguide, comprising: forming a lower clad layeron a base board; forming an insulation layer, having a core-formingthrough-hole therein, on the lower clad layer; filling the through-holein the insulation layer with a core material; forming a core part bypatterning the core material received in the through-hole; and formingan upper clad layer in the rest through-hole except for the core partand on the insulation layer.
 7. The method according to claim 6, whereinthe forming the core part comprises: layering a transparent releasablefilm on the insulation layer having the through-hole filled with thecore material, to thus flatten the core material; selectively exposingthe core material through a pattern mask; and removing the transparentreleasable film and developing the exposed core material, thus forming aplurality of core patterns.
 8. The method according to claim 7, whereinthe transparent releasable film includes polyethylene terephthalate. 9.The method according to claim 6, wherein the forming an insulation layercomprises: layering the insulation layer on the lower clad layer; andremoving a portion of the insulation layer to form the core-formingthrough-hole.
 10. The method according to claim 6, wherein the formingan insulation layer comprises: preparing the insulation layer; removinga portion of the insulation layer to form the core-forming through-hole;and layering the insulation layer having the core-forming through-holeon the lower clad layer.
 11. The method according to claim 6, whereinthe base board includes any one of a metal layer for forming a circuit,a rigid printed circuit board, a flexible printed circuit board and arigid-flexible printed circuit board.
 12. The method according to claim6, wherein the insulation layer is selected from a group consisting of athermosetting resin, a thermoplastic resin, a reinforcingmaterial-impregnated thermosetting resin, a reinforcingmaterial-impregnated thermoplastic resin, and a combination thereof. 13.A method of manufacturing a printed circuit board for an opticalwaveguide, comprising: forming a lower clad layer on a base board;forming a molding film, having a core-forming through-hole therein, onthe lower clad layer; filling the through-hole in the molding film witha core material; forming a core part by patterning the core materialreceived in the through-hole; removing the molding film; and forming anupper clad layer on the lower clad layer such that the upper clad layersurrounds the core part.
 14. The method according to claim 13, whereinthe forming a core part comprises: layering a transparent releasablefilm on the molding film having the through-hole filled with the corematerial, to thus flatten the core material; selectively exposing thecore material through a pattern mask; and removing the transparentreleasable film and developing the exposed core material, thus forming aplurality of core patterns.
 15. The method according to claim 14,wherein the transparent releasable film includes polyethyleneterephthalate.
 16. The method according to claim 13, wherein the forminga molding film comprises: layering the molding film on the lower cladlayer; and removing a portion of the molding film to form thecore-forming through-hole.
 17. The method according to claim 13, whereinthe base board includes any one of a metal layer for forming a circuit,a rigid printed circuit board, a flexible printed circuit board and arigid-flexible printed circuit board.
 18. The method according to claim13, wherein the molding film includes a photo-sensitive resist film. 19.The method according to claim 13, wherein the molding film includes areleasable film.